When using BGA (Ball Grid Array) packages as components on electronic circuit boards an inspection of solder joints of these components is necessary in many cases. Solder bonds of BGA packages are hidden under the package or circuit, and hence a reliable inspection of solder joints has been a difficult task for many companies assembling circuit boards. Hence, during the two past decades, several X-rays systems have been developed for inspection of BGA packages. Using the results of such inspections, assembler companies have been able to better control the quality and condition of the solder joints.
However, the complexity, the limitations, such as the lack of capability of detecting “cold” solder joints, cracks, thermal stress, flux agent residues, etc., and the high cost of X-ray systems, typically in the range of EUR40 000 to EUR100 000, have made visual inspection systems be an attractive alternative or complement to X-ray systems. The need for visual inspection of BGA and similar packages is constantly increasing within the electronic circuit manufacturing industry since more and more BGA, MicroBGA, CSP and Flip-Chip packages are designed and assembled on PCBs (Printed Circuit Boards). The visual inspection systems are becoming efficient, cost effective and reliable besides the X-ray systems, even bringing advantages that the X-ray systems do not offer.
Optical systems for inspection of BGA joints like Ersascope manufactured and sold by Ersa GmbH or VPI-optical Inspection System manufactured by Metcal in Menlo Park, Calif., have been on the market for a few years. However, the video microscopes according to the prior art can, due to their designs, only be used stationarily in laboratories and they have not such a degree of integration that they can be used as mobile equipment, without extra requirements such as of being connected to a stand and/or to external illumination sources and/or other necessary accessories or devices.
U.S. Pat. No. 6,580,501 for Cannon and assigned to Ersa GmbH discloses stationary apparatus for visual inspection of concealed solder joints, the apparatus including a lens head, an ocular unit and an image transmission unit for transmitting the image from the lens head to the ocular unit and having the basic structure and shape of an industrial or medical endoscope. The lens head comprises a housing having a recess in which a light deflecting prism is mounted. An illumination device has light exits located at opposite sides of the prism, the light exits being the free ends of the fibers of a glass fiber bundle, the fibers connected to a single external light source at their other ends. The light exits issue light in directions parallel to the surface of the PCB which is to be inspected.